1. Field of the Invention
The present invention relates to an Electron Emission Display (EED) device which can adjust a pulse width of a data signal supplied to data electrode lines of a panel, and more particularly, to an EED device which can actively adjust a pulse width of a data signal using a predefined waveform or a predefined pointer according to an active pulse width of a horizontal synchronization signal.
2. Description of the Related Art
An Electron Emission Display (EED) device includes an EED panel and a driver. When the driver supplies a positive voltage to an anode of the EED panel, if the positive voltage is supplied to a gate electrode and a negative voltage is supplied to a cathode electrode, electrons are emitted from the cathode. The emitted electrons are accelerated toward the gate electrode and converged into the anode. Then, the electrons collide with fluorescent cells disposed in front of the anode, thereby emitting light.
An EED device includes an EED panel and a driver. The driver includes a video processor, a panel controller, a scan driver, a data driver, and a power supply unit.
The video processor converts an external analog video signal into a digital signal to generate an internal video signal, for example, R, G and B video data, a clock signal, and horizontal and vertical synchronization signals.
The panel controller generates data driving control signals and scan driving control signal according to the internal video signal outputted from the video processor. The data driver processes the data driving control signal and outputs a display data signal to data electrode lines of the EED panel. The scan driver processes the scan driving control signal SS and supplies the processed signal to scan electrode lines.
The power supply unit supplies an electrical potential of 1 to 4 KV to the video processor, the panel controller, the scan driver, the data driver, and an anode electrode of the EED panel. The data electrode lines are connected to cathode electrodes of the EED panel and the scan electrode lines are connected to gate electrodes. When a positive voltage is supplied to the anode, if the positive voltage is supplied to the gate electrodes through the scan electrode lines and a negative voltage is supplied to the cathode electrodes through the data electrode lines, then electrons are emitted from the cathode. The emitted electrons are accelerated toward the gate electrodes and converged into the anodes. Then, the electrons collide with fluorescent cells disposed in front of the anodes, thereby emitting light.
Gray level control methods for adjusting the luminance of the EED panel include a Pulse Width Modulation (PWM) method which controls an amount of time that a data signal pulse is supplied and Pulse Amplitude Modulation (PAM) method which controls a voltage amplitude of data signal pulse.
In the PWM method, a reference signal generated by a reference signal generator is counted by a gray level signal generator and a gray level signal counted at every proper reference signal is outputted to the data driver. The data driver outputs a PWM-ed data signal to the data electrode lines according to the gray level signal.
In a modulation module which modulates the pulse width of the data signal in the EED device adopting the PWM scheme, the reference signal generator generates the reference signal for modulating the pulse width of the data signal according to a high speed system clock. An active period (+or − period of the waveform) of the pulse waveform or one period of the pulse is fixed so that the waveform of the reference signal is suitable for the horizontal synchronization signal supplied to the EED panel.
The gray level signal generator counts the reference signal to generate the gray level signal. The gray level signal is a signal that is counted from just after a clear signal has been inputted, every time that the reference signal is supplied. The gray level signal has a waveform in which a pulse width increases according to the count or a waveform in which a position of the pulse is shifted in a horizontal direction according to the count. The gray level signal is inputted to a modulation comparator, and the modulation comparator compares the video data with the gray level signal. If the video data and the gray level signal have the same data value, the modulation comparator outputs a signal having a corresponding pulse width. Therefore, the pulse width of an output data signal is adjusted according to size of the video signal. As a result, data signals whose light intensity have been adjusted by the different pulse width are outputted to the data electrode lines. The modulation comparator is generally provided inside the data driver.
In case of PWM, the light intensity is controlled according to the pulse width of the data signal, and in case of PAM, the light intensity is controlled by adjusting the voltage amplitude of the data signal. PAM has an advantage of low power consumption and high output luminance. However, even if the voltage is increased slightly, the control of the luminance according to the voltage difference is difficult owing to a rapid increase of the output current. For these reasons, PWM is widely used.
In the EED device using PWM, the gray level depends on the horizontal synchronization signal. Whenever the horizontal synchronization signal is supplied, data is supplied to one line (that is, one row) of the EED panel. All minimum gray level data and maximum gray level data are supplied to one line while one horizontal synchronization signal is supplied. In case of the EED device using 256 gray levels, a width corresponding to an active pulse width of one horizontal synchronization signal is used as a maximum gray level.
In an EED device having a fixed modulation pulse width with respect to such gray levels, if the gray levels are leveled up, gray levels exceeding the active pulse width of one horizontal synchronization signal cannot be expressed. Thus, the luminance of the panel is degraded. Also, in an EED device that does not require high gray levels, if the active pulse width of one horizontal synchronization signal is made narrow, it is necessary to redesign the system to match with the gray levels according to the new modulation pulse width.
The horizontal synchronization signal and the reference signal are dependent on the high frequency system clock and the gray level signals are generated by counting the reference signal. The EED device uses 256 gray levels and the panel expresses 0-255 gray levels. All gray levels are present within the active pulse width of the horizontal synchronization signal and the maximum gray level (255 gray level) is also present within the active pulse width of the horizontal synchronization signal. However, when gray levels exceed 255 gray level owing to the modification of the system, or when the active pulse width of the horizontal synchronization signal is reduced, it is impossible to express the gray levels exceeding the active pulse width of the horizontal synchronization signal. Therefore, problems occur in that the expression range of the gray level is reduced and the luminance is lowered.